/**
 * @file   1041.cpp
 * @author Shuang Hu <hsmath@ubuntu>
 * @date   Wed Apr 14 00:36:25 2021
 * 
 * @brief  PAT advanced,problem 1041:UNIQUE
 * @time Only need 5 minutes!
 * 
 */

#include <iostream>
#include <map>
#include <vector>
using namespace std;
int main(){
    int N;
    cin>>N;
    vector<int> arr;
    for(int i=0;i<N;i++){
	int num;
	cin>>num;
	arr.push_back(num);
    }
    map<int,int> stat;
    for(int i=0;i<N;i++){
	stat[arr[i]]++;
    }
    bool flag=false;
    for(int i=0;i<N;i++){
	if(stat[arr[i]]==1){
	    cout<<arr[i]<<endl;
	    flag=true;
	    break;
	}
    }
    if(flag==false){
	cout<<"None"<<endl;
    }
}
